<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        
    </style>
</head>
<body>
    
</body>
<script>

    var a = "千锋，好！";
    console.log(a);
    console.log(window.a);

    function fn(){
        window.b = 20;
    }
    fn()
    console.log(b)


</script>
</html>